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Using global Sentinel-1 radar backscatter data, we systematically map the locations of glaciers with surge-type activity during 2017–22. Patterns of pronounced increases or decreases in the strongest backscatter between two winter seasons often indicate large changes in glacier crevassing, which we treat here as a sign of surge-type activity. Validations against velocity time series, terminus advances and crevassing found in optical satellite images confirm the robustness of this approach. We find 115 surge-type events globally between 2017 and 2022, around 100 of which on glaciers already know as surge-type. Our data reveal a pronounced spatial clustering in three regions, (i) Karakoram, Pamirs and Western Kunlun Shan (~50 surges), (ii) Svalbard (~25) and (iii) Yukon/Alaska (~9), with only a few other scattered surges elsewhere. This spatial clustering is significantly more pronounced than the overall global clustering of known surge-type glaciers. The 2017–22 clustering may point to climatic forcing of surge initiation. [ABSTRACT FROM AUTHOR]

Monitoring avian migration within subarctic regions of the globe poses logistical challenges. Populations in these regions often encounter the most rapid effects of changing climates, and these seasonally productive areas are especially important in supporting bird populations—emphasizing the need for monitoring tools and strategies. To this end, we leverage the untapped potential of weather surveillance radar data to quantify active migration through the airspaces of Alaska. We use over 400 000 NEXRAD radar scans from seven stations across the state between 1995 and 2018 (86% of samples derived from 2013 to 2018) to measure spring and autumn migration intensity, phenology and directionality. A large bow-shaped terrestrial migratory system spanning the southern two-thirds of the state was identified, with birds generally moving along a northwest–southeast diagonal axis east of the 150th meridian, and along a northeast–southwest axis west of this meridian. Spring peak migration ranged from 3 May to 30 May and between, 18 August and 12 September during the autumn, with timing across stations predicted by longitude, rather than latitude. Across all stations, the intensity of migration was greatest during the autumn as compared to spring, highlighting the opportunity to measure seasonal indices of net breeding productivity for this important system as additional years of radar measurements are amassed. [ABSTRACT FROM AUTHOR]

In this work, we evaluate landfast sea ice dynamics using ground-based radar interferometry. During two field campaigns in Utqiaġvik, Alaska, we collected three ∼24-h series of measurements on 16 May 2012 and 21–23 April 2021 using the Gamma portable radar interferometer (GPRI). These data enable examination of progressive strain of landfast ice on the sub-cm scale. The results indicate near spatially uniform divergence strains exceeding 10−6 in response to an increase in offshore winds from 0 to 7 m s−1. Exceptions to uniform divergence are grounded ridges with either negligible or reduced motion. We also track uniform vertical shifts in response to cm-scale sea level change correlated with NOAA model tidal predictions. We evaluate and take steps to remove contributions from moisture variability, thereby reducing potential errors from atmospheric effects to less than 5 mm. The results suggest that the GPRI can be a valuable tool for monitoring ice-covered coastal zones. The system has possible applications for monitoring tides and ocean surges and tracking small-scale deformation of otherwise stationary ice that can lead to fracture and destabilization. • We resolve wind-induced ice strain over kilometers with cm-scale accuracy. • We track vertical displacement of sea ice in microtidal environment. • We obtain minute-scale temporal resolution and sub-meter range resolution. • Allows accurate location and timing of episodic events e.g., cracks and detachments. • Atmospheric effects can be mitigated by removing phase change from static targets. [ABSTRACT FROM AUTHOR]

Spring runoff measurements of Arctic watersheds are challenging given the remote location and the often dangerous field conditions. This study combines remote sensing techniques and field measurements to evaluate the applicability of synthetic aperture radar (SAR) to defining spring breakup of the braided lower Kuparuk River, North Slope, Alaska. A statistical analysis was carried out on a time series (2001 - 10) of SAR images acquired from the European Remote Sensing Satellite (ERS-2) and the Canadian RADARSAT satellite, as well as on measured runoff. On the basis of field information, the SAR images were separated into pre-breakup, breakup, and post-breakup periods. Three variables were analyzed for their suitability to bracket the river breakup period: image brightness, variance in brightness over the river length, and a sum of rank order change analysis. Variance in brightness was found to be the most reliable indicator. A combined use of that variance and sum of rank order change appeared promising when enough images were available. The temporal resolution of imagery served as the major limitation in constraining the timing of the hydrologic event. Challenges associated with spring runoff monitoring and the sensitive nature of SAR likely resulted in an earlier detection of surficial changes by the remote sensing technique compared to the field runoff observations. Given a sufficient temporal resolution, SAR imagery has the potential to improve the spatiotemporal monitoring of Arctic watersheds for river breakup investigations. [ABSTRACT FROM AUTHOR]